Preparation, crystal structure and luminescence properties of a novel single-phase red emitting phosphor CaSr₂(PO₄)₂:Sm³⁺,Li⁺

Single-phase CaSr₂(PO₄)₂:Sm³⁺,Li⁺ phosphors were prepared <i>via</i> a high-temperature solid-state method under air. The powder X-ray diffraction patterns, scanning electron microscopy images, photoluminescence spectra, and concentration-dependent emission spectra were measured to characterize the as-prepared phosphors and luminescence decay curves. The results showed that the CaSr₂(PO₄)₂:Sm³⁺,Li⁺ phosphors exhibited red luminescence, and the emission spectra of the phosphors consisted of four sharp peaks at around 565, 601 (the strongest one), 647 and 707 nm. The optimum doping concentration of Sm³⁺ ions was 0.09 (mol concentration), and the mechanism of energy transfer among Sm³⁺ ions was defined to be quadrupole-quadrupole (q-q) interactions using Dexter's theory. The Blasse concentration quenching method was used to determine the critical distance <i>R</i> _c for energy transfer among Sm³⁺ as 10.99 Å. The results indicate that the as-prepared phosphors have good thermal stability with an activation energy of 0.773 eV <i>via</i> temperature-dependent emission spectra. Therefore, CaSr_2-2<i>x</i> (PO₄)₂:<i>x</i>Sm³⁺,<i>x</i>Li⁺ materials can be used as red-emitting phosphors for UV-pumped white-light emitting diodes.